The present invention relates generally to devices, systems and methods for the operation of breathing apparatuses in multiple modes and, particularly, to devices, systems and methods for operating a breathing apparatus with different pressures with a facepiece in different modes of operation.
The following information is provided to assist the reader to understand the invention disclosed below and the environment in which it will typically be used. The terms used herein are not intended to be limited to any particular narrow interpretation unless clearly stated otherwise in this document. References set forth herein may facilitate understanding of the present invention or the background of the present invention. The disclosure of all references cited herein are incorporated by reference.
A self contained breathing apparatus (“SCBA”) is a device used to enable breathing in environments which are immediately dangerous to life and health (IDLH). For example, firefighters wear an SCBA when fighting a fire. The SCBA typically has a harness supporting an air tank which is connected to a facepiece, all of which are worn or carried by the user. The tank typically contains air or gas under high pressure (2200 psi-4500 psi) and is connected to a first stage regulator which reduces the pressure to about 80 psi. The SCBA usually has a second stage regulator that has an inlet valve which controls the flow of air for breathing between the air tank and the facepiece. Typically, the inlet valve controls the flow of air through the second state regulator in response to the respiration of the user. Such respiration-controlled regulator assemblies are disclosed, for example, in U.S. Pat. Nos. 4,821,767 and 5,016,627.
Typically, a diaphragm divides the regulator assembly into an inner chamber having a pressure corresponding to the pressure within the facepiece of the SCBA and an outer chamber having a pressure corresponding to the pressure in the surrounding environment, which is typically ambient pressure. The diaphragm is coupled to an actuating mechanism which opens and closes the inlet valve. The user's respiration creates a pressure differential between the inner and outer chambers of the regulator assembly which, in turn, causes displacement of the diaphragm thereby controlling (that is, opening and closing) the inlet valve mechanism. As a result, such regulators are often called pressure demand regulators.
The facepiece of the SCBA is typically maintained at a positive pressure as compared to the surrounding environmental pressure to, for example, prevent toxic gases and vapors in the surrounding environment from entering the facepiece. This positive pressure can, for example, be facilitated by biasing the diaphragm with a spring.
Combination breathing apparatuses are devices that combine two or more types of National Institute for Occupational Safety and Health (NIOSH) approved breathing apparatuses into a single integrated system. A currently available example of a combination breathing apparatus is the dual-purpose FIREHAWK® SCBA available from Mine Safety Appliances Company of Pittsburgh, Pa. That device integrates an SCBA and an airline respirator. Another example of a combination device is the DUO-FLO® apparatus, available from Mine Safety Appliances Company, which combines an airline respirator and a gas mask (a type of air purifying respirator). A combination SCBA and PAPR is described in U.S. Patent Application Publication No. US 2004/0182395 published Sep. 23, 2004 and U.S. Patent Application Publication No. US 2005/0022817 published Feb. 3, 2005.
To meet NIOSH requirements, the exhalation valve for powered air purifying respirators (PAPRs) and air purifying respirators (APRs) must meet low inhalation resistance requirements of 20 mm of water at 85 lpm (liters per minute) flow. That result is typically achieved by using a simple rubber check valve in the exhaust valve. However, use of a simple rubber check valve cannot enable the facepiece to hold air pressure above ambient pressure. The exhalation valve for a pressure demand respirator such as an SCBA or an airline respirator normally includes a rigid valve umbrella with a spring that biases the valve against a valve seat. Use of a biased valve umbrella enables air pressure above ambient to be held in the facepiece at all times, which is a NIOSH requirement for pressure demand respirator. Combining an APR and/or a PAPR with an SCBA or airline respirator, while meeting all NIOSH breathing test requirements, requires that the exhalation valve meet the low resistance requirement of APR and PAPR exhalation resistance and also allowing pressure within the facepiece to be higher than ambient pressure for SCBA or airline pressure demand operation.
Several attempts have been made to provide for switching between respiration modes in breathing apparatuses. For example, United Kingdom Patent Application No. GB 2,264,646 discloses a breathing apparatus including a connector 10 of a pressurized air connection that moves a piston rearward within a fitting 15. A connected cable passing through a sleeve 18 causes a piston to move and change the length of a spring loading an exhalation valve of the breathing apparatus, thereby changing the load on the exhalation valve. Two actions are required to switch respirator modes. First, the user must disconnect the supply line which “turns-off” the air regulator. Second, the user must push the hose end fitting or connector 10 into the facepiece receptacle which switches the exhalation valve from a “pressure demand” mode to a “demand” mode. The user must also disconnect the pneumatic supply line from the air supply and reconnect the supply line to a parking position in the facemask. The disconnection of the supply line can introduce contamination into the hose fittings if done in a contaminated atmosphere. There is also the possibility that the user of the breathing apparatus of GB 2,264,646 will be subjected to high exhalation resistance while in demand mode if the user fails to park the supply line into the receptacle upon removing it from the pressure source or if the air supply runs-out.
European Patent No. EP 0 667 171 discloses a breathing apparatus in which mechanical abutment of an abutment member on a connection for an air pressure connection causes a pin to move to cause a first spring to place force on the diaphragm. In the case of the attachment of a filter or a vacuum rather than the pressurized air connection, there is no similar abutment member to contact the pin. In the case of attachment of a filter or a vacuum, a second spring exerts force on the diaphragm with less force than the first spring. The user of the breathing apparatus of European Patent No. EP 0 667 171 must be in a clean environment to switch exhalation valve modes as such a switch requires removing the air purifying or air supplying device from the admitting duct.
Italian Patent No. IT 1,227,248 apparently discloses a breathing apparatus (see, for example, FIG. 1) in which pressure is used to inflate a bellows to change force exerted upon a diaphragm of an exhalation valve via an exhalation valve spring. The pressure is apparently provided by the low pressure air supplied by a second stage regulator or “demand valve”. Providing pressure from the second stage regulator results in expansion and contraction of the bellows as the user breathes, potentially causing the exhalation valve spring to change compression and thereby changing the pressure required to open the exhalation valve as the user inhales and exhales.
It remains desirable to develop improved devices, systems and methods for operating (and preferably automatically operating) a breathing apparatus with different pressures within a facepiece in different modes of operation wherein the pressure within the facepiece is different depending upon the mode of operation.